This invention relates to hot runner injection molding and more particularly to such apparatus having an elongated cooled mold core and core lock member with matching abutting parts of their surfaces having a reverse taper.
Circulating cooling fluid through elongated mold cores to reduce cycle time is well known. Molds with long mold cores for making products such as pill vials, cosmetic containers, medical beakers and beverage bottle preforms have a problem known as core shift. As seen in U.S. Pat. No. 5,061,174 to Gellert which issued Oct. 29, 1991, the rear part of the outer surface of the mold core and the abutting surface of the surrounding stripper ring are usually slightly tapered outwardly towards the rear end to facilitate assembly. When the high injection pressure impacts against a number of mold cores in a large mold, it can force the mold cores slightly rearwardly which loosens their tapered seats in the stripper rings and creates space for the mold cores to shift slightly to one side or the other. This lateral shifting of the mold cores results in uneven filling of the cavities and forms a non-concentric product which is unacceptable. This is particularly a problem for bottle preforms, as the blown bottle may sit crookedly or bulge out on one side.
Another problem with elongated cooled mold cores is that the high injection pressure can cause them to flex slightly. Thus, both the core shift and flexing problems limit injection pressure and prevent faster filling and shorter cycle times.